During the lifetime of a patient, it may be necessary to perform a total shoulder replacement procedure on the patient as a result of, for example, disease or trauma. In a total shoulder replacement procedure, a humeral component having a head portion is utilized to replace the natural head portion of the arm bone or humerus. The humeral component typically has an elongated intramedullary stem which is utilized to secure the humeral component to the patient's humerus. In such a total shoulder replacement procedure, the natural glenoid surface of the scapula is resurfaced or otherwise replaced with a glenoid component that provides a bearing surface for the head portion of the humeral component.
As alluded to above, the need for a shoulder replacement procedure may be created by the presence of any one of a number of conditions. One such condition is the deterioration of the patient's scapula in the area proximate to the glenoid surface as a result of, for example, glenohumeral arthritis. In such a condition, the erosion of the patient's scapula is generally observed posteriorly on the glenoid surface. Such erosion of the scapula renders treatment difficult, if not impossible, with a conventional glenoid prosthesis.
In order to treat a condition in which a portion of the scapula has been eroded, a number of glenoid prostheses have heretofore been designed. Such glenoid prostheses, known generally as augmented glenoid prostheses, have a posterior edge that is thicker than the corresponding anterior edge.
In FIG. 1, a heretofore-designed augmented glenoid component 100 is shown. The glenoid component 100 has a metallic backing component 102 and plastic insert 104. The thickness of the metallic backing component 102 gradually increases from an anterior edge 106 to a posterior edge 108 thereof thereby creating a relatively smooth, arcuate-shaped medial surface 110 from which a number of posts or pegs 112 extend.
The design of the augmented glenoid component 100, however, has a number of associated drawbacks. For example, the relatively smooth, arcuate-shaped medial surface 110 may over time lead to loosening of the augmented glenoid component 100, thereby potentially necessitating additional surgical procedures to replace or reseat the component 100. Further, due to the configuration of the medial surface 110, a relatively high shear load is created along the implant-to-bone interface when the component 100 is implanted. The presence of a high shear load along the implant-to-bone interface tends to also cause loosening of the component 100 over a period of time. Post-operative loosening is the largest cause of failures of implanted glenoid components.
In FIG. 2 another heretofore-designed augmented glenoid component 100A is shown. The glenoid component 100A has a single component plastic body 102A. The thickness of the plastic body 102A gradually increases from an anterior edge 106A to a posterior edge 108A thereof thereby creating a relatively smooth, arcuate-shaped medial surface 110A from which a number of posts or pegs 112A extend. The design of this augmented glenoid component 100A, however, suffers from at least the same drawbacks as the glenoid component 100.
In FIG. 3 another heretofore-designed augmented glenoid component 100B is shown. The glenoid component 100B also has a single component plastic body 102B. The thickness of the plastic body 102B gradually increases from an anterior edge 106B to a posterior edge 108B thereof thereby creating a relatively smooth medial surface 110B from which a keel 114B extends. The design of this augmented glenoid component 100B, however, suffers from at least the same drawbacks as the glenoid components 100 and 100A.
What is needed therefore is an augmented glenoid component that overcomes one or more of the above-mentioned drawbacks. What is further needed is an augmented glenoid component that is less susceptible to postoperative loosening relative to heretofore designed glenoid components.
Attempts have been made in the prior art to provide for a glenoid implant that accommodates posterior erosion. In fact, a device has been designed for augmented glenoid component to accommodate posterior erosion. This attempt at finding a glenoid component to accommodate erosion has provided for generally compressive load and minimize the shear load earlier prior art devices. This device is described in U.S. Pat. No. 6,699,289 to Iannotti et al incorporated herein by reference to its entirety.
Referring now to FIG. 4, a scapula 116 is shown with posterior wear 118. Glenoid component 120 as shown in phantom includes an articulating surface 122, which is symmetrically positioned with respect to the scapula 116. Thus, shown in FIG. 4, the glenoid component 120 is required to be thicker or higher at the portion of the scapula 116 with the posterior defect 118. As shown in FIG. 4, the load factor 124 for the glenoid component 120 is in a different orientation than the load factor 126 normal to the worn scapula 116. Thus, the glenoid component 120 positioned on the scapula 116 includes a force vector 128 that is in shear and that my cause loosening of the glenoid component.
Referring now to FIG. 5, the scapula 116 may be prepared by a buttress or step 130 such that there are two support surfaces 132 and 134 formed on the glenoid fossa of the scapula 116. Preparation of the glenoid cavity is shown in U.S. Pat. No. 6,699,289 to Iannotti et al which is hereby incorporated herein by reference to its entirety. Referring now to FIG. 6, support load vectors 136 are shown parallel load force vectors 138 of the glenoid component 140.
The device of Iannotti provides for and improvement of the load distribution placed upon the glenoid component. This device provides generally for a one piece glenoid component, which is optimum for one particular posterior erosion pattern. A need remains for a posterior augmented glenoid component that may accommodate a wide variety of posterior erosion conditions that may minimize the quantity and types of components necessary to provide for a wide variety of patient needs.